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Subject[PATCH 3.12 1/5] dm: fix AB-BA deadlock in __dm_destroy()
Date
From: Junichi Nomura <j-nomura@ce.jp.nec.com>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

commit 2a708cff93f1845b9239bc7d6310aef54e716c6a upstream.

__dm_destroy() takes io_barrier SRCU lock (dm_get_live_table) and
suspend_lock in reverse order. Doing so can cause AB-BA deadlock:

__dm_destroy dm_swap_table
---------------------------------------------------
mutex_lock(suspend_lock)
dm_get_live_table()
srcu_read_lock(io_barrier)
dm_sync_table()
synchronize_srcu(io_barrier)
.. waiting for dm_put_live_table()
mutex_lock(suspend_lock)
.. waiting for suspend_lock

Fix this by taking the locks in proper order.

Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Fixes: ab7c7bb6f4ab ("dm: hold suspend_lock while suspending device during device deletion")
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
drivers/md/dm.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 5a0b1742f794..de444d3ae293 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2444,14 +2444,14 @@ static void __dm_destroy(struct mapped_device *md, bool wait)
* do not race with internal suspend.
*/
mutex_lock(&md->suspend_lock);
+ map = dm_get_live_table(md, &srcu_idx);
if (!dm_suspended_md(md)) {
dm_table_presuspend_targets(map);
dm_table_postsuspend_targets(map);
}
- mutex_unlock(&md->suspend_lock);
-
/* dm_put_live_table must be before msleep, otherwise deadlock is possible */
dm_put_live_table(md, srcu_idx);
+ mutex_unlock(&md->suspend_lock);

/*
* Rare, but there may be I/O requests still going to complete,
--
2.10.1
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